Data storage devices are known which use various forms of media such as an optical disc, a magnetic tape, and a semiconductor circuit. Among those devices, the hard disk drive (HDD) has come into wide use as a storage device of a computer and is one of the storage devices that are indispensable for current computer systems. Because of its superior characteristics, the use of the HDD is not limited to computers, but is rapidly expanding to moving image recording/reproducing devices, vehicle navigation systems, cell phones, removable memories used in digital cameras etc., and other devices.
A magnetic disk used in the HDD has plural concentric tracks. Plural pieces of servo data having address information and data sectors including user data are recorded on each track. A head element unit accesses a desired data sector according to the address information of servo data, whereby data writing to or data reading from the data sector can be performed.
Each data sector has a data address mark indicating a start position of its user data. If a data address mark cannot be detected, the user data of the corresponding data sector cannot be read out. A format for solving this problem is known in which each data sector has plural data address marks (refer to Japanese Patent Publication No. 10-255400 “Patent document 1”, for example). Even if the first data address mark cannot be detected, the user data of the data sector concerned can be read out by performing reading by use of the following data address mark and performing data correction processing.
There may occur a case that one data sector is divided into two or more sections by servo data. Such a data sector is called a split sector. An HDD using two data address marks has two data address marks in each section of a split sector. In reading out the user data of each section, one data address mark included therein is used.
There exists a channel circuit which is different from a channel circuit of Patent document 1 which continues data read processing by automatically using a data address mark that is different from a data address mark that has caused an error. The former channel circuit performs sector read processing using only data address marks that are specified in advance. In the channel circuit which uses specified data address marks, data processing is stopped upon occurrence of an error in detecting a data address mark. A controller is required to inform the channel circuit of a data address mark to be used in the next retry. Where as described above a sector is divided into two sections, the split sector has four data address marks. When an error has occurred in detecting a data address mark, the controller informs the channel circuit of a data address mark that is different from the one that has caused the error.
However, if the controller receives only the information that an error has occurred in detecting a data address mark, the controller is required to make three retries at the maximum. A specific example will be described below. Assume that the first section of a split sector has first and second data address marks and the second section has third and fourth data address marks, and that the channel circuit uses the first and third data address marks as default marks.
When an error has occurred in detecting a data address mark, the controller makes retries in order for three combinations, that is, first and fourth data address marks, second and fourth data address marks, and second and third data address marks. Therefore, the controller makes three retries at the worst case.
To increase the capacity of an HDD, it has been proposed to increase the data size of each data sector. The current size of each data sector is 512 bytes. Increasing the data size from this value makes it possible to decrease the amount of data other than user data and thereby allows the magnetic disk to store more user data. More specifically, it has been proposed to set the data size of each data sector at 4 Kbytes.
When the data size of each data sector is increased as described above, the number of sections of each split sector increases and the number of data address marks increases accordingly. The increase in the number of data address marks results in increase in the number of combinations of data address marks for which retry processing is performed upon occurrence of an error in detecting a data address mark and hence is a factor in causing delay of the retry processing.